Known pre-transfer baffles comprise shapes that have been optimized over the years for performance at the lower end of the range of media weights. Over time, however, users of xerographic devices have demanded systems capable of handling heavier and larger media. More recent systems permit sheet lengths from 22.5 inches to 26 inches, and some recent systems permit sheet weights as high as 350 grams per square meter (gsm). Larger, heavier sheets exhibit more drag through the pre-transfer baffle, and as such print quality defects are generated on the sheets causing, for example, longitudinal bands across the image.
Known systems attempt to accommodate two different weight medias using a single geometry, i.e., the known pre-transfer arrangement. Lighter weight paper requires a steep angle of attack relative to the bottom of the photoreceptor belt which forces the paper into contact with the belt. If the angle of attack is too shallow, the paper flutters, and only a partial image transfer occurs. Contrarily, heavier weight paper is stiffer and when the trailing edge impacts the photoreceptor belt a perturbation is caused resulting in band formation in the image. Additionally, perturbations can be caused by impact of the lead edge on belt, in other words, as the lead edge contacts the belt during its approach.
A variety of defects can occur due to the foregoing perturbations. For example, perturbations may cause shift of the media relative to the belt thereby causing image offset relative to the media. Electrostatic issues may arise as the media impacts the belt and causes a transient in the belt. As the media passes through the baffle, the trail edge of the media may stick to the baffle thereby shifting the media relative to the belt. The foregoing defects may also result in banding of the image deposited on the media as depicted in FIG. 1. Media 10 comprises printed image 12 having bands 14 appearing therein.
U.S. Pat. No. 4,739,362 (the '362 patent) discloses an improved transfer station baffle arrangement comprising first and second baffles. The first baffle includes a curved sheet supporting surface imparting a bow to sheets passing thereby. The second baffle normally biases the sheets against the first baffle and is biasable out of position with respect to the first baffle. The '362 patent fails to address the need to alter the angle of approach of the media as the media contacts the photoreceptor belt.
U.S. Pat. No. 8,155,572 (the '572 patent) proposes a dual position media registration transport and media pre-transfer baffle geometry to enable printing on heavy weight media materials, e.g., for packaging. Known media pre-transfer geometry limits processing heavy weight media due to the inherent “S” baffle pre-transfer geometry. The packaging industry requires heavy weight media, e.g., greater than 350 gsm. The '572 patent enables a two position pre-transfer baffle assembly. The standard pre-transfer baffle assembly position allows normal weight media to enter the pre-transfer baffle assembly with the normal “S” shape, which allows all performance specifications to be maintained. Trained operators can also change several items related to the pre-transfer baffle assembly to a second position, which allows heavy weight media to properly pass. The second position provides a straightened path and enables heavy weight media and packaging materials to enter the pre-transfer area. This enables the printing of these media and materials, which could not be processed through the “S” shape of the standard pre-transfer baffle assembly position. The foregoing arrangement fails to fully accomplish the desired outcome, i.e., efficient, user independent operation of a pre-transfer baffle.